Painting on my model doesn't work
For Blender Internal Follow this quick step below and Save the file in UV Editor


UV unwrap the mesh.
Default material
In the UV Editor -> Click on New Image  (width x height and give a file name as(abc)) -> ok
In Uv Editor -> Image -> Save as Image F3 give a name -> click ok.
Add a New material -> In the Texture Tab click on New
Below in the Textures -> Image -> Select from drop down image saved in UV (abcc)
Switch to Texture Paint -> Now you can paint




For cycles Follow this quick step below and Save the file in UV Editor


UV unwrap the mesh.
Default material
In the UV Editor -> Click on New Image  (width x height and give a file name as(abc)) -> ok
In Uv Editor -> Image -> Save as Image F3 give a name -> click ok.
In the Material -> Surface -> Color -> Change to Image texture -> Select the created image (abc) from drop down.
Switch to texture paint -> Now you can paint.